The present invention is related to a radio communication apparatus such as a mobile communication appliance for performing a mobile communication in a portable telephone, and also related to a transmission power control method in this radio communication apparatus.
In general, mobile communication appliances such as portable telephone units are equipped with functions capable of controlling transmission power of own units based upon distances between base stations and mobile stations while information is transmitted. In the multiple access type communication system for multiplexing a plurality of communication channels, a transmission power control for maintaining power of a signal reached to a base station at a constant value is necessarily required in order to increase a frequency utilization efficiency while reducing interference occurred between communication channels.
More specifically, in a CDMA (Code Division Multiple Access) type mobile communication appliance with employing a spread spectrum communication technique, since a single frequency band is commonly used by a plurality of users, there are great possibilities that a signal having low transmission power is masked by a signal having high transmission power, namely a so-called xe2x80x9cfar/near problemxe2x80x9d. Thus, the following problem would occur. That is, a signal transmitted from another station may function as an interference signal wave to cause a line quality to be deteriorated. To solve such a problem, conventionally, various sorts of transmission power control techniques have been studied. In particular, the transmission power control system by the closed loop is known as the transmission power control system capable of tracing such interference signals which are instantaneously varied. More specifically, in the CDMA system, the transmission power control with a high linearity and a wide dynamic range (for instance, 70 to 80 dB) is required. Furthermore, in the wide-band CDMA (W-CDMA), higher precision of the transmission power is required when signals having high power are transmitted, and thus, higher precision of the transmission power control operation is further required. This wide-band CDMA system has been considered as the mobile communication system for the next generation.
FIG. 19 is a flow chart for showing an example of the conventional transmission power control method by the closed loop. This transmission power control method may be used in the transmission power control and other controls by open/close loop controls executed based upon the IS-95 rule of TIA (Telecommunications Industry Association).
In a communication is established between a base station and a mobile station, the mobile station determines a transmission power control bit based on reception power of a reception signal wave (desirable signal wave) sent from the base station (S101), inserts this transmission power control bit into a transmission signal, and then transmits the resultant transmission signal to the base station. The base station receives the signal transmitted from the mobile station, extracts the transmission power control bit from the reception signal (S105), and then controls a variable power amplifier of the own station in accordance with the instruction of this transmission power control bit (S106).
Similarly, the base station determines a transmission power control bit based on reception power of a reception signal wave sent from the mobile station (S104), inserts this transmission power control bit into a transmission signal, and then transmits the resultant transmission signal to the mobile station. The mobile station receives the signal transmitted from the base station, extracts the transmission power control bit from the reception signal (S102), and then controls a variable power amplifier of the own station in accordance with the instruction of this transmission power control bit (S103).
Since such a transmission power control is carried out, it is possible to keep the reception power substantially constant in both the base station and the mobile station irrespective of the distance between the base station and the mobile station.
For example, in xe2x80x9cTRANSMISSION POWER CONTROL METHOD AND SPREAD SPECTRUM COMMUNICATION APPARATUS WITH USING CONTROL METHOD THEREOFxe2x80x9d described in Japanese Laid-open Patent Application No. Hei-8-32513 opened in 1996, the transmission power is controlled based upon the transmission power control amount corresponding to a total number of the transmission power bit having the same bit value which is continuously received. As a consequence, the increased or decreased step of the transmission power are increased while the continuous reception time has elapsed in order to follow the rapid variation in the communication path.
In the above-explained conventional transmission power control method, since the transmission power control operation is carried out by a single transmission power control system (variable power amplifier), the high-precision variable power amplifier is required in order that, in particular, such a transmission power control operation having a high linearity and a wide dynamic range is carried out. This transmission power control operation is required for the CDMA system Also, the variable power amplifier amplification function must be carried out in high precision.
However, when a variable power amplifier is controlled in high precision with employment of such a high-precision variable power amplifier, the following problems will occur. That is, a circuit scale is increased, a power consumption amount is increased, and an entire apparatus would be made in high cost. Also, it is practically difficult to employ only one variable power amplifier for realizing a wide-range gain control, while maintaining high precision. Furthermore, in the case that a mobile station is a portable telephone, while the transmission power is controlled in high precision, the power consumption is required to be suppressed by reducing the circuit scale (namely, circuit is made simple and compact). As a result, considering the power consumption, the portability, and the apparatus cost, there are various difficulties in order to realize the high-precision transmission power control over the wide range by using the conventional transmission power control method.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a compact radio communication apparatus operable under low power consumption, and a transmission power control method in such a radio communication apparatus, while realizing a transmission power control means with having a simple arrangement and operable under low power consumption, and increasing precision of a transmission power control operation.
To achieve the above-described object, a radio communication apparatus, according to the present invention, comprises a transmission power control function capable of controlling transmission power to a communication counter station, comprising: a plurality of variable power amplifying means for amplifying transmission power; and variable: power amplifying-controlling means for controlling the plurality of variable power amplifying means in either a serial control manner or a parallel control manner over an entire control range to thereby perform a variable amplifying-controlling operation.
Preferably, the variable power amplifying-controlling means compares own transmission power stored therein with a predetermined threshold value, and then, performs the serial control manner with respect to the plurality of variable power amplifying means over the entire control range based upon the comparison result.
Preferably, the variable power amplifying-controlling means includes: control bit extracting means for extracting a transmission power control bit transmitted from a communication counter station; transmission power storing means for updating the own transmission power stored thereinto based upon the transmission power control bit; comparing means for comparing the own transmission power stored thereinto with a predetermined threshold value; and controlling-outputting means for sending out a control signal to the plurality of variable power amplifying means based upon the comparison result so as to perform the serial control manner with respect to the plurality of variable power amplifying means over the entire control range.
Alternatively, the variable power amplifying-controlling means includes: control bit extracting means for extracting a transmission power control bit transmission power control bit transmitted from a communication counter station; transmission power storing means for updating the own transmission power stored thereinto based upon the transmission power control bit; and controlling-outputting means for sending out a control signal to the plurality of variable power amplifying means based upon the own transmission power stored thereinto so as to perform the serial control manner with respect to the plurality of variable power amplifying means over the entire control range.
Further, preferably, as the plurality of variable power amplifying means, two variable power amplifiers series-connected to each other are provided; and the variable power amplifying-controlling means performs the variable amplifying-controlling operation in either the serial control manner or the parallel control manner over the entire control range with respect to the two variable power amplifiers.
Also, a variable amplifier may be further employed at a prestage of the plurality of variable power amplifying means; the variable power amplifying-controlling means further performs the variable amplifying-controlling operation in either the serial manner or the parallel manner among the variable power amplifying means with respect to the variable amplifier.
A transmission power control method in a radio communication apparatus, according to the present invention, for controlling transmission power to a communication counter station, comprising: a variable power amplifying-controlling step for controlling a plurality of variable power amplifying means over an entire control range either in a serial manner or a parallel manner so as to perform a variable amplifying-controlling operation.
Preferably, in the variable power amplifying-controlling step, own transmission power stored thereinto is compared with a predetermined threshold value, and then, the serial control manner with respect to the plurality of variable power amplifying means is performed over the entire control range based upon the comparison result.
Also, the variable power amplifying-controlling step may contains: a control bit extracting step for extracting a transmission power control bit transmitted from a communication counter station; a transmission power storing step for updating the own transmission power stored thereinto based upon the transmission power control bit; a comparing step for comparing the own transmission power stored thereinto with a predetermined threshold value; and a controlling-outputting step for sending out a control signal to the plurality of variable power amplifying means based upon the comparison result so as to perform the serial control manner with respect to the plurality of variable power amplifying means over the entire control range.
Alternatively, the variable power amplifying-controlling step may contains: a control bit extracting step for extracting a transmission power control bit transmitted from a communication counter station; a transmission power storing step for updating the own transmission power stored thereinto based upon the transmission power control bit; and a controlling-outputting step for sending out a control signal to the plurality of variable power amplifying means based upon the comparison result so as to perform the serial control manner with respect to the plurality of variable power amplifying means over the entire control range.
Further, preferably, in the variable power amplifying-controlling step, the variable amplifying-controlling operation is carried out in either the serial control manner or the parallel manner among the variable power amplifying means with respect to a variable amplifier provided at a prestage of the plurality of variable power amplifying means.
In accordance with the radio communication apparatus of the present invention and also the transmission power control method of this radio communication apparatus, a plurality of variable power amplifying means are controlled either in the serial control manner or the parallel control manner over the entire control range so as to perform the variable amplifying-controlling operation. In this case, the fluctuations occurred in both edge portions of the variable range of each of the variable power amplifying means are preferably controlled to be absorbed by way of either the serial control manner or the parallel control manner for a plurality of variable power amplifying means. As a result, the linearity within the control range can be improved, and the high-precision transmission power control with a simple arrangement and over a wide range can be carried out, as compared in the general control case that one variable power amplifying means is controlled. Also, since these plural variable power amplifying means are controlled in either the serial manner or the parallel manner, the carrier-to-noise ratio (C/N) of the transmission signal in the radio communication apparatus can be improved, and also the communication can be made simple and compact. As a result, while the control precision of the transmission power is maintained, the circuit scale can be reduced. In particular, when the serial, or parallel control manner is employed in the mobile station, since the circuit can be made simple and compact, the portability can be improved, and the power consumption can be suppressed.
Also, the variable amplifying-controlling operation is further carried out either in the serial control manner or in the parallel control manner among a plurality of variable power amplifying means with respect to the variable amplifier provided at the prestage of the plural variable power amplifying means. Also, in this case, the linearity within the above-described control range can be improved, and since either the serial control manner or the parallel control manner is additionally provided with respect to the variable amplifier, the C/N can be further improved.